Many light projectors have a light source that uniformly illuminates an image formation chip, such as a DMD, LCoS, LCD or reflective LCD (or film) that subtractively modulates the incoming light in order to create a target image. Such projectors typically 1) cannot exceed a peak luminance set by the optical power of the light source, the projected image size, and the reflectivity of the image screen, and 2) have a dynamic range or contrast that is limited by the image formation device, for example film, or digital devices like LCD, LCOs or DMD imaging chips.
Light projectors vary in their capability to produce target images with specified luminance and chromaticity values. The range of capabilities stem from technological limitations related to maximum peak luminance (optical output of the light source) to lowest black-level and hence contrast (contrast of the included image formation technology), to chromatic purity and colour gamut (governed either by the filters applied to a broadband source or to the wavelength of, for example, a laser light source), as well as uniformity and noise specifications. Some projectors can produce light output with limited contrast, for example reaching a peak luminance of 100 cd/m2 and a black level of 1 cd/m2, and hence a contrast of 100:1. Other projectors can reach brighter highlights (by increasing the light source power), and/or deeper black levels (using higher contrast image formation technology). In some systems, very deep black levels can be achieved by modulating the image twice (“dual modulation”). The contrast or dynamic range of a projector can be dynamically adjusted by inserting an iris or aperture in the light path, whose light blocking may be driven in response to image content.
The type of and requirements of image or video content to be reproduced on a projector can vary significantly in time over the course of a presentation of image or video content. The presentation could, for example, comprise presentation of a movie in a cinema, a live performance that uses projectors, or projection of light by adaptive (image-) projector headlights while driving in different conditions in a vehicle. For example a movie might begin with a dark, high contrast, black and white scene, and later contain bright and low contrast scenes with pure colors. While driving at night, an adaptive car headlight might be required to project a uniform, and low contrast light field on an empty road outside the city, but within the city be required to produce a very high contrast, bright image to highlight stop signs, avoid illuminating upcoming cars (casting a shadow in that region) or signaling information on the road.
High brightness, high dynamic range projectors are often more expensive than standard lower dynamic range projectors for similar average light (power) outputs. One reason for this is that achieving better black levels often requires more elements within the system (for example dual modulation designs that use cascaded, light attenuating elements). Another reason is that achieving higher peak luminance on the same screen requires more light-source power in the projector.
There remains a need for good ways to control a projection system to reproduce image content having characteristics that vary significantly over time (e.g. characteristics such as dynamic range, black level, maximum luminance, color saturation) as in the examples above. Such ways would beneficially provide advantages such as reducing power requirements, providing good black level, and/or providing bright highlights.
There remains a need for light projection systems that offer one or both of higher image quality and better cost efficiency.
There remains a need for practical and cost effective projection systems suitable for projecting patterns such as images, desired lamp illumination patterns, and the like. There is a particular need for such systems that are able to faithfully display content having characteristics that change significantly over time (e.g. systems called upon to display bright low-contrast images at some times and to display dark images with bright highlights at other times).